Conventionally, developments of a transmission system and an optical fiber that use Wavelength Division Multiplexing (WDM) have been actively advanced with the objective of increasing the data transmission rate in backbone and/or long-distance systems. The characteristics such as suppression of the nonlinear effect or chromatic dispersion control have been demanded for optical fibers for WDM transmission. In recent years, optical fibers in which the dispersion slope is decreased for a system called metro (metropolitan area network) with a span of about several kilometers or optical fibers that are subjected to virtually no loss increase due to Hydroxyl Group (OH) have been proposed.
When introduction of optical fibers to offices and homes (Fiber To The Home; FTTH) is taken into consideration, characteristics different from those for the above-described optical fibers for transmission are required. In the case of wiring the fibers in the building or the house, there is the possibility that a very small bending with a   diameter such as 30 mm or 20 mm occurs. Furthermore, when the extra length of the cable is stored, it is very important that a loss increase does not occur even if the cable is wound around a small radius. That is, it is a very important characteristic for the optical cable for FTTH to resist a small-radius bend. The connectivity with optical fibers (many of which are SMFs with a normal bandwidth of 1.3 μm) used from the base station to the building or to the house is also an important point.
Patent Document 1: U.S. Patent Application Publication No. 2004/0213531
Patent Document 2: PCT International Publication No. WO 01/27667 pamphlet
Non-Patent Document 1: I. Sakabe, et al., “Enhanced Bending Loss Insensitive Fiber and New Cables for CWDM Access Network,” Proceedings of the 53rd IWCS, pp. 112-118 (2004)
Non-Patent Document 2: S. Matsuo et al., “Bend-insensitive and low-splice-loss optical fiber for indoor wiring in FTTH,” OFC 2004, ThI3
Non-Patent Document 3: Sato et al., “Optical Fiber Conforming to Bending around Small Radius for Optical Access,” The Institute of Electronics, Information and Communication Engineers (IEICE) Society Conference 2003, B-10-30
Non-Patent Document 4: Ikeda et al., “Low Bending Loss Optical Fiber with Reduced Splice Loss,” Technical Report of IEICE, OCS 2003-43
Non-Patent Document 5. Zhou et al., “A Study on Application of Photonic Crystal Fiber to Wiring in Homes and Buildings,” Technical Report of IEICE, OFT 2002-81
Non-Patent Document 6: Yao et al., “A Study on Commercialization of Holey Fiber,” Technical Report of IEICE, OFT2002-82